1. Field of Invention
The invention relates to light microscopy, and, more particularly, to differential interference contrast microscopy.
2. Discussion of Related Art
Differential interference contrast (DIC) light microscopy is commonly employed to observe structure and motion in unstained living cells and isolated organelles. DIC microscopy utilizes a beam-shearing interference system in which an illumination beam is sheared into two beams having a spatial separation typically less than the resolution of the microscope. The two beams are recombined after passing through a specimen to produce an interference image related to optical phase gradients of the specimen.
A DIC microscopy can produce a monochromatic shadow-cast image of a specimen that displays a lateral gradient of the optical path presented by the specimen, i.e., a lateral phase gradient associated with the specimen. Those regions of the specimen where the optical path increases along a reference direction can appear brighter, while regions where the path differences decrease appear in reverse contrast. As the gradient of the optical path grows steeper, image contrast is increased.
Images are typically dependent on beam-shear direction because specimen gradients in a direction perpendicular to a beam-shear direction generally do not contribute to image contrast. A type of reflection microscope, which includes two DIC microscopes operating at different wavelengths, but sharing a single objective through a beam splitter, can help to reveal more specimen detail.
Video-processing techniques can be utilized to enhance contrast and/or remove background signals (such as fixed image noise due to dust particles or other imperfections in the optical system) by subtraction of a reference image with no specimen.